1. Field of the Invention
This invention relates in general to certain new and useful improvements in apparatus and method for applying weld material to crankshafts and other metal parts, and more particularly, to an apparatus and method of the type stated in which a welding torch is capable of moving with respect to, and maintaining a closely spaced relationship to axially offset portions of a metal part, as for example the crank pins and journals of a crankshaft during rotation thereof.
2. Brief Description of the Prior Art
In recent years with the advent of more sophisticated hydrocarbon combustion engines, it has been necessary to provide an improved apparatus and method for welding the crankshafts of these engines. In many cases, the crankshafts are constructed so that they can be mounted in an engine block with a high degree of close tolerence with respect to other moving components. Consequently, these crankshafts require a considerable amount of time to maintain and thus are quite expensive.
In many cases, the bearings of the crankshaft, as well as the crank pins, become worn, and it is oftentimes necessary to build up the metal thickness of the crankshaft by adding a weld material in order to accomodate oversized bushings or the like in the engine block. Further, during maintenance and inspection procedures, it oftentimes becomes apparent that weakened areas may exist in the crankshaft and it is necessary to repair the weakened crankshaft by adding a weld material to various portions or to the entire crankshaft, in order to obviate the costly replacement of the shaft.
There have been several proposals to provide crankshaft welding apparatus. One such proposed apparatus is more fully described in U.S. Pat. No. 3,205,336 to Joseph Smith. While this patent discloses an apparatus which obviates many of the heretofore existing problems in crankshaft welding apparatus, it did not obviate the requirement of having a welding torch orbit, or at least follow axially offset portions of the crankshaft during the welding operation.
U.S. Pat. No. 3,978,310 to William Gleason also discloses an apparatus for arc welding crankshafts. In the Gleason patent, the problem of having the arc welding torch head follow axially offset portions of the crankshaft was obviated to some extent. However, the mechanism employed in the Gleason patent which permitted the torch to follow axially offset portions of the head was quite complex, thereby making the apparatus difficult to operate, relatively unprecise, and quite costly. The apparatus in the Gleason patent disclosed a carriage member which appeared to shift vertically in a somewhat "dancing" manner and has been characterized in the trade as a "dancing" carriage. Further, the mechanism for adjusting positional movement of the carriage to enable the torch head to closely follow the rotatable movement of the axially offset portions of the crank shaft was difficult to operate and not relatively effective. Consequently, the overall effectiveness of the apparatus taught in the Gleason patent was relatively low.
In addition to the foregoing, rotation of the crankshaft in the apparatus described in the Gleason patent was quite difficult and time consuming. If one of the mounting chucks which retained the crankshaft on the apparatus was released, the synchronism required in the apparatus was lost. Furthermore, it is difficult to maintain synchronism in the apparatus described in the Gleason patent when changing from one rod general diameter to another, particularly when the crankshafts are preheated normally to about 450.degree. F. for welding. The apparatus of the Gleason patent also employed a counter-weight in the vertically shiftable carriage in the Gleason patent apparatus. This counter-weight is substantial and generally in the area of at least 300 lbs. which caused vibration when moved and decreased materially the overall efficiency of the apparatus.
One of the significant problems in the apparatus of the type taught in the Gleason patent is that the tip of the welding torch did not follow a truly circular path during the orbiting movement thereof. This was due to the fact that the employed carriage arrangement caused the torch to tip or shift slightly angularly during movement thereof. As a result, weld material was applied in greater thickness to one portion of the crankshaft than another circumferentially second portion thereof.